Receptors of various types and various toxins serve to modulate ion channels and generation of second messengers, including cyclic nucleotides, diacylglycerides, arachidonic acid and phosphatidic acid. Calcium, sodium, potassium, and magnesium ions after translocation through ion channels or by transport proteins can cause activation of release processes, contractile proteins, adenylate and guanylate cyclase, phosphodiesterases, protein kinases, phospholipases, ATPases and other enzymes. Modulatory interactions or "cross-talk" occurs both between the second messenger systems and the ion transport systems. Maitotoxin, a marine polyether, increases phosphoinositide breakdown in a variety of cells, apparently through activation of a membrane calcium channel. The maitotoxin-activated calcium channel does not appear identical to any know calcium-channel, including the so-called calcium release-activated calcium (CRAC) channel although both channels are blocked by certain imidazoles (SKF 96365, miconazole, clotrimazole). Loperamide is one of the most potent blockers of maitotoxin-elicited channels, but causes an apparent enhancement of influx through the CRAC-channels that open after receptor-mediated or thapsigargin-elicited depletion of IP3-sensitive intracellular pools of calcium in that a variety of cell types. The effect of loperamide is unique, high dependent on structure, and not readily reversed by imidazoles. Epiboxidine, a methylisoxazole analog of epibatidine, retains high activity at ganglionic and central neuronal nicotinic receptors and is a potent analgetic with reduced toxicity compared to epibatidine. Spiropyrrolizidines and pseudophrynaminol represent a new classes of noncompetitive blockers of nicotinic channels. The most potent central site of action of the putative antiaddictive agent ibogaine was found to be noncompetitive blockade of ganglionic nicotinic-receptor channels. Ibogaine was highly effective against analgesia triggered by activation of central neuronal nicotinic receptors. The profile of affinities of all possible ring-fluorinated dopamines at different dopamine and noradrenergic receptors was determined. Other studies involving biogenic amines include the localization and role of catechol-0- methyltransferase in human mammary carcinoma, hamster kidney and rat dental pulp.